Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$109.35	13.559%	$124.1768	$124.18	$124.20	$124.20
Purchase #2	$139.40	3.394%	$144.1312	$144.13	$144.15	$144.10
Purchase #3	$46.90	7.734%	$50.5272	$50.53	$50.55	$50.50
Purchase #4	$72.74	7.744%	$78.373	$78.37	$78.35	$78.40
Purchase #5	$126.88	13.304%	$143.7601	$143.76	$143.75	$143.80
Purchase #6	$159.67	4.436%	$166.753	$166.75	$166.75	$166.80
Purchase #7	$33.80	9.700%	$37.0786	$37.08	$37.10	$37.10
7 purchase totals =	$688.74		$744.7999	$744.80	$744.85	$744.90